1. Field of the Invention
The present invention relates to a power supply apparatus configured to supply a power supply voltage to a device under test.
2. Description of the Related Art
FIG. 1 is a circuit diagram which shows a configuration of a test apparatus according to a related art. A test apparatus 2r is configured to supply a power supply voltage VOUT to a device under test (DUT) 1, and to measure a load current IOUT that flows through the DUT 1 in the operating state.
The test apparatus 2r includes: a power supply apparatus 4r configured to generate the power supply voltage VOUT to be supplied to the DUT 1; and a current measurement circuit 6r configured to measure the current IOUT that flows through the DUT 1. A smoothing decoupling capacitor CL is arranged in the vicinity of the DUT 1 between a power supply terminal P2 and a ground terminal. An output terminal P1 of the power supply apparatus 4r and the power supply terminal P2 of the DUT 1 are connected via a cable of a certain length. Such a transmission path that comprises such a cable functions as a parasitic impedance 3 that affects the power supply apparatus 4r. 
The power supply apparatus 4r includes a D/A converter 8 and a voltage source 10.
The D/A converter 8 receives, from an unshown signal processing unit, a digital value DIN that corresponds to the target value of the output voltage VOUT, and outputs an analog input voltage VIN. The voltage source 10 generates the power supply voltage VOUT that corresponds to the input voltage VIN. The voltage source 10 includes an operational amplifier A1, a buffer A2, a buffer A3, a phase compensation circuit 12, an input resistor Ri, and a feedback resistor Rf. The voltage source 10 is configured as an inverting amplifier, and is configured to invert the negative input voltage VIN so as to output the positive power supply voltage VOUT. Specifically, the voltage source 10 stabilizes its output voltage VOUT to the target level obtained by multiplying the input voltage VIN by a negative coefficient. With the power supply apparatus 4r shown in FIG. 1, a feedback operation is performed so as to satisfy the following Expression.VOUT/Rf+VIN/Ri=0  (1)
Thus, the target value of the output voltage VOUT is represented by the following Expression (2).VOUT=−Rf/Ri×VIN  (2)
The current measurement circuit 6r includes a current detection resistor Rm, an amplifier 22, and an A/D converter 24. The current detection resistor Rm is arranged on a path of the output current IOUT. A voltage drop, which is proportional to the output current IOUT, occurs at the current detection resistor Rm. The amplifier 22 amplifies the voltage drop that occurs at the current detection resistor Rm. The A/D converter 24 converts the voltage thus amplified by the amplifier 22 into a digital value. The digital value thus converted exhibits a value that is proportional to the output current IOUT.
In many cases, between a product (set) mounting the DUT 1 in practice and the test apparatus 2r, there is a difference in the capacity and the performance of a power supply circuit (which will be referred to as the “set power supply”) which is used to supply a power supply voltage to the DUT 1. In order to solve such a problem, the user desires a test apparatus 2r that supplies the power supply voltage VOUT to the DUT 1 in the test operation for the DUT 1 in conditions that are more similar to those of the actual product. In order to meet such a requirement, there is a demand for the test apparatus 2r to have a function for emulating the performance of such a set power supply.